Climate Pessimists Were Right

By

Sharon Begley

Updated Feb. 9, 2007 12:01 a.m. ET

In the great climate debate, those who argue that the world is not warming, or that if it is, it's warming naturally, don't like being called "greenhouse skeptics." They're none too fond of "climate contrarians" or "greenhouse deniers," either. Instead, James Taylor of the Heartland Institute, a libertarian research and advocacy group in Chicago, calls himself a "climate realist."

Now, some 20 years after scientists first warned that greenhouse gases would alter the planet's climate in dangerous ways, it is possible to assess who is being more realistic. Starting with the first report of the U.N.-sponsored Intergovernmental Panel on Climate Change in 1990, critics have called its projections foolishly apocalyptic. Some earlier reports did miss the mark on a few counts, but not in the way the "realists" contend. In some cases, the reality of climate change has been even worse than the alarming forecasts.

A number of greenhouse projections were spot-on, while others underestimated how radically gases such as carbon dioxide, emitted when fossil fuels burn, would alter climate by trapping heat in the atmosphere. The world's surface temperature has increased one-third of a degree Celsius since 1990 -- the upper end of projections, according to scientists led by Stefan Rahmstorf of the Potsdam Institute for Climate Research, in Germany. Their analysis appeared last week in the online issue of the journal Science.

With sea level, climate change has outpaced the projections. Satellite measurements show that the waters around the world rose 3.3 millimeters per year, averaged from 1993 to 2006. The IPCC foresaw 2 millimeters per year. "The main message of our [analysis] is to those who have claimed that IPCC is exaggerating climate change or is painting unduly grim future scenarios," says Dr. Rahmstorf. "Unfortunately, this is not true; the real climate system is changing as fast as, or in some components even faster than, expected by IPCC."

Ice in arctic seas also is melting faster than expected. (Though that doesn't raise sea levels; melting ice on land does.) It now covers 11% less area than it did in 1978, and 20% less in the late summer. "That's about double the mean model projection," notes physicist Joseph Romm, author of a new book on global warming, "Hell or High Water."

To be sure, IPCC scientists keep refining their forecasts, narrowing the range of predicted sea-level rise and global warming, and in some cases settling on a less-dire "best estimate." The first report, in 1990, had 3&deg;C as the best estimate for global warming by 2100; the best estimate had fallen to 2&deg;C in the 1995 report and is now 2&deg; to 4&deg;.

The statistic that heartened Mr. Taylor was the best estimate of sea-level rise by 2100. It was 60 centimeters in the 1990 report and 50 centimeters in the 1995 report, with a range of 15 to 95 centimeters. The current report, released in summary form last week, gives a range of 18 to 60 centimeters by the century's end. "We see a retraction of the most extreme global-warming scenarios" in regard to sea level, says Mr. Taylor. "It bears out what climate realists have said" about the Cassandra-ish tendencies of climatologists who study the greenhouse effect.

Whatever 2100 brings, however, sea-level rise today has exceeded forecasts. That doesn't mean it will continue to; sea-level rise is the most difficult greenhouse effect to predict. But so far, ice sheets at the top and bottom of the world -- in Greenland and Antarctica -- have behaved in ways models failed to predict, disintegrating faster than even the 2001 IPCC report anticipated. "We don't have models of ice-sheet behavior that we have faith in," says Michael Oppenheimer of Princeton University, an IPCC author. "They didn't predict what the ice sheets have done over the past 15 years."

The models fall short in their representation of ice streams, rivers of ice that (despite being solid) flow from ice sheets out to sea. The streams have been speeding up, carrying ice to the ocean more quickly than expected. "There has been a revolution in our knowledge of how major ice sheets respond to climate change," says Kevin Trenberth of the National Center for Atmospheric Research, Boulder, Colo. "This isn't incorporated fully into the models, but observations show [the response is] happening, and faster than expected."

The IPCC got it right when it projected more downpours and droughts. Already, precipitation falls less often, but when it rains it pours. The basic idea that global average temperatures would rise has also been spot-on, with 11 of the past 12 years among the 12 warmest since instruments began recording temperatures in 1850. Because climate models can't zero in on extreme weather events, though, except to say they will occur more often, they failed to foresee disasters like the 2003 heat wave in Europe that killed some 26,000 people.

In focusing on global averages, climate projections make the coming changes sound gradual, slow, sedate. That's how ozone loss was originally portrayed, too; no one foresaw the sudden "ozone hole" over Antarctica. It remains to be seen if climate reality, too, can suddenly tip into an extreme.

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